Phenoxybenzamine

Phenoxybenzamine

Clinical data
Trade names	Dibenzyline
AHFS/Drugs.com	Monograph
MedlinePlus	a682059
Pregnancy category	C (U.S.)
Routes of administration	Oral
ATC code	C04AX02 (WHO)
Pharmacokinetic data
Biological half-life	24 hours
Identifiers
IUPAC name (RS)-N-benzyl-N-(2-chloroethyl)-1-phenoxypropan-2-amine
CAS Number	59-96-1 Y
PubChem (CID)	4768
IUPHAR/BPS	7268
DrugBank	DB00925 Y
ChemSpider	4604 Y
UNII	0TTZ664R7Z Y
KEGG	D08358 Y
ChEMBL	CHEMBL753 Y
ECHA InfoCard	100.000.406
Chemical and physical data
Formula	C18H22ClNO
Molar mass	303.826 g/mol
3D model (Jmol)	Interactive image
Chirality	Racemic mixture
SMILES ClCCN(C(COc1ccccc1)C)Cc2ccccc2
InChI InChI=1S/C18H22ClNO/c1-16(15-21-18-10-6-3-7-11-18)20(13-12-19)14-17-8-4-2-5-9-17/h2-11,16H,12-15H2,1H3 Y Key:QZVCTJOXCFMACW-UHFFFAOYSA-N Y

Phenoxybenzamine (marketed under the trade name Dibenzyline) is a non-selective, irreversible alpha blocker.

It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma. It has a slower onset and a longer-lasting effect compared with other alpha blockers.

It was also the first alpha blocker to be used for treatment of benign prostatic hyperplasia, although it is currently seldom used for that indication due to unfavourable side effects.

It has been used in the treatment of hypoplastic left heart syndrome.

It is also used in complex regional pain syndrome (CPRS) type 1 due to its anti-adrenergic affects. It has shown to be beneficial if used in the first 3 months of the CRPS diagnosis.

Phenoxybenzamine has long been known to block ejaculation without affecting semen quality or ability to achieve orgasm, which could make it an effective male contraceptive. This effect is completely reversible, and is believed to be the result of alpha-1 adrenoceptor blockade in the longitudinal muscles of the vas deferens. As of 2008, research was underway to identify possible drug candidates that share this effect but act specifically on the reproductive tract, unlike phenoxybenzamine.

Phenoxybenzamine is used as an anti-hypertensive due to its efficacy in reducing the vasoconstriction caused by epinephrine (adrenaline) and norepinephrine. Phenoxybenzamine forms a permanent covalent bond with adrenergic receptors. Based on known information about the structures of these receptors, it likely involves attack by the cysteine at position 3.36 in transmembrane helix 3 to form a stable linkage. Thus, it remains permanently bound to the receptor, preventing adrenaline and noradrenaline from binding. This causes vasodilatation in blood vessels, due to its antagonistic effect at the alpha-1 adrenoceptor found in the walls of blood vessels, resulting in a drop in blood pressure. A side effect of phenoxybenzamine is reflex tachycardia.